You shouldn't copy-paste the comment from Mahout.  At the very least, paraphrase:

```
A simple implementation of the Lanczos algorithm (link) for eigenvalue computation.

Like the Mahout implementation, only the matrix*vector step is parallelized.

Eigendecomposition is used to extract the eigenvalues from the sub (desired_rank*desired_rank)
sub-matrix.  The sub-matrix is re-orthogonalized against previous eigen-vectors after every pass.
This portion of the process is sequential and written in Python...
```